1. Field of the Invention
The present invention relates to a monitoring system, recording medium storing a monitoring program and a monitoring method which are for monitoring whether or not switching of lines, switching of devices, control of a plant, control of an information system, etc. are completed normally.
2. Description of Related Art
An object of communication devices, information processing devices, and other similar devices is to raise the communication quality. For this object, prior art has an auxiliary line separate from a main line, which is provided to a subscriber. When there is a failure in the main line in prior art, the main line is switched to the auxiliary line. Prior art attains the object by thus switching the lines.
A line controlling device switches the main line and the auxiliary line. The controlling device decides to make a switch depending on the state of communications over the main line and the auxiliary line each, such as the presence or absence of a line failure and the line state. For this purpose, the controlling device monitors the communication state. The controlling device chooses which one of the lines is to be the operating line based on the monitored communication state. A control signal is therefore sent from the controlling device to a commanded-to-switch-lines device.
In the line switching control, the controlling device sends a line switching command to the commanded-to-switch-lines device. The commanded-to-switch-lines device follows the received command and line switching control is executed in the device. After the line switching is completed normally, the commanded-to-switch-lines device sends a notification of completion of the line switching to the controlling device.
The controlling device monitors a response time, which starts at the moment a line switching command is sent and ends at the moment a line switching completion notification is received from the commanded-to-switch-lines device. The controlling device judges whether the response is received within an estimated normal time or not. Based on the judgment, the controlling device detects a communication trouble between the controlling device and the commanded-to-switch-lines device, and detects an anomaly, a failure, or the like in the commanded-to-switch-lines device.
The response time between the controlling device and the commanded-to-switch-lines device includes a fixed time and a variable time. A fixed time is a physically fixed time that is determined by the wiring length, a bit delay in the device, or the like. A variable time is a time that is varied by fluctuations in a wiring delay between the controlling device and the commanded-to-switch-lines device due to external, environmental factors such as temperature, or by a physical bit delay difference in devices of different types connected to each other. Accordingly, the response time is the sum of a fixed time and a variable time. The controlling device uses a fixed delay time and, as a variable time, an offset value to monitor the response time. The offset value represents a fluctuating time of the response time due to variable factors in the system. The controlling device sets, as a maximum response time value, a value obtained by adding the offset value to an estimated response time and sets, as a minimum response time value, a value obtained by subtracting the offset value from the estimated response time. The controlling device treats the time range between the maximum response time value and the minimum response time value as a range in which a response time is judged as normal. A response time outside of this time range is deemed as a sign of a line trouble. Hereinafter, a line trouble may be referred to as NG. A monitored response time coincides with this range of time. The relation described above is expressed as follows:
A maximum or minimum response time value that is not NG:C(t)=t±dt  (1)
t: a physical transmission time between the controlling device and the commanded-to-switch-lines device (fixed time)
dt: an offset value to account for a fluctuation in transmission time between the controlling device and the commanded-to-switch-lines device FIG. 5 is given as an example of response time monitoring according to Expression (1). FIG. 5 is a graph showing the relation between the monitoring count and the response time according to prior art.                [Patent document 1] JP 2000-116034 A        [Patent document 2] JP 04-86049 A        
The controlling device of prior art monitors the response time using t, which represents a fixed time, and dt, which is the value of fluctuation in transmission delay due to external factors, as shown in Expression (1). However, the conventional monitoring method which uses Expression (1) has a problem in that line troubles are detected in succession (NG judgment is made repeatedly) when the external environment changes more than foreseen by the administrator or the like, causing a relative increase or decrease in delay time.
Therefore, to improve the accuracy of measuring the response time, the maximum and minimum response time values, which are expressed by t±dt, are calculated precisely by making the maximum and minimum response time values conform to the external environment. The allowance of dt, which is a fluctuating value, is reduced by a relative increase or decrease in delay time due to a change in external environment or the like. Accordingly, a relative increase or decrease in delay time due to a change in external environment or the like will result in detection of line troubles (NG judgment) even when the fluctuation is within the initially estimated range. Thus the accuracy of measuring the response time depends on how closely t±dt can conform to the external environment.
One of methods that aim to improve the accuracy of measuring the response time is to measure a response time until a time in question or to measure response times at regular cycles. According to this method, the measured times are accumulated in a memory for a certain period of time, and a value obtained by averaging the times accumulated in the memory is set as t. This method minimizes the fluctuating value (dt). Thus the method improves the accuracy of monitoring the response time.
In another method of prior art, measured values of the response time are accumulated as frequency distribution of measured times, and a measured response time value that is the maximum distribution value is set as t. This method minimizes the fluctuating value (dt). Thus the method improves the accuracy of monitoring the response time.
The response time in the conventional methods can be expressed as follows (in these methods, a physical transmission time between the controlling device and the commanded-to-switch-lines device which is a fixed time is used as an actually measured value):
A maximum or minimum response time value that is not NG:C(t)=T1±dt  (2)
T1: a response time until a time in question or the average value of response times measured at regular cycles and accumulated, or a response time obtained from frequency distribution of measured times
dt: an offset value to account for a fluctuation in transmission time between the controlling device and the commanded-to-switch-lines device
In these conventional methods, measured values of the response time within a certain time range are accumulated in a memory. The conventional monitoring methods use the response times accumulated in the memory to obtain a maximum or minimum response time value that is not NG. Accordingly, the conventional monitoring methods have a drawback of being incapable of detecting whether a response time is NG or not at an instant.
In addition, the conventional monitoring methods cannot follow a relative delay time fluctuation resulting from constant changes in external environment as shown in FIG. 6, which illustrates an example of the response time monitoring according to Expression (2). FIG. 6 is a graph showing the relation between the monitoring count and the response time according to prior art. The conventional monitoring methods thus have a problem in that the response time cannot be detected accurately.
The present invention has been made in view of the circumstances described above, and an object of the present invention is therefore to provide a monitoring system, a recording medium storing a monitoring program and a monitoring method which achieve more reliable monitoring control by improving the accuracy of measuring a response time to a switching command in line switching, device switching, plant control, information system control, etc.